This invention relates to a particulate lead titanate ceramic a method of making the ceramic and to composite materials containing the particulate lead titanate ceramic.
Lead titanate (PbTiO.sub.3) is a ferroelectric of a perovskite structure and is used in a wide variety of applications as piezoelectric or pyroelectric materials. Due to its higher piezoelectric charge constant d.sub.h (d.sub.33 +2d.sub.31) and piezoelectric stress constant g.sub.h (=d.sub.h /.epsilon.) in under water conditions as compared with other ferroelectrics such as lead titanate-zirconate, lead titanate attracts particular attention in applications to underwater acoustic transducers such as hydrophones.
There has been an increasing demand for flexible, low density piezoelectric materials which exhibit excellent acoustic matching with water in efficiently receiving or generating acoustic or ultrasonic waves and which have strength sufficient to withstand water pressures in deep sea bottoms. In meeting the above demand, the present inventors have proposed a piezoelectric composite material which includes lead titanate powder dispersed in an organic matrix of a synthetic rubber or synthetic resin (Japanese Laid Open Publication No. 57-87680).
Conventionally, lead titanate powder has been prepared by calcining a mixture of TiO.sub.2 and PbO with a predetermined composition at about 1050.degree. C. The lead titanate particles thus obtained have various indeterminate shapes so that they are oriented at random when dispersed in an organic matrix. For this reason, even when an external electrical field is applied to the lead titanate particles for poling thereof and for regularizing their poling directions, parts of them fail to be sufficiently oriented. This adversely affects the piezoelectric properties of the lead titanate powder.